1. Field of the Invention
The present invention relates to a power conversion system.
2. Related Art
A motor drive device that controls the drive of a machine or the like utilizes an alternating current power supply (a commercial power supply or the like), a direct current power supply (a battery or the like), or the like, as a power input source. Furthermore, in order to increase the power utilization efficiency, the motor drive device may have a function of returning power generated in the motor when applying a brake to the action of the machine or the like (regenerative power) to the input source.
There is known a power conversion system that, in order to drive, or the like, some load, generates direct current power from an alternating current/direct current power supply, converts the direct current power into alternating current power, and has a function of returning regenerative power to the power supply side, the heretofore described motor drive device being one example, although this example is not limiting.
A power conversion system used in the heretofore described motor drive device, or the like, has a converter unit and an inverter unit. The converter unit generates an arbitrary direct current power based on the input power source, and provides the direct current power to the inverter unit. Herein, as the converter unit is compatible with a regenerative operation, it can cause alternating current power or direct current power to flow in either direction between the converter unit and input power source. That is, in the case of an alternating current power supply, the converter unit can cause alternating current power to flow in either direction between the converter unit and input power source. In the case of a direct current power supply such as a battery, the converter unit can cause direct current power to flow in either direction between the converter unit and input power source.
The inverter unit converts the direct current voltage generated by the converter unit into alternating current power of an arbitrary frequency and voltage, and carries out a drive or braking operation of the motor.
The converter unit controls the voltage value of the direct current voltage that is the output thereof. That is, the value is maintained so that the output voltage does not drop due to causing power from the input power source to flow to the inverter side when the inverter unit drives the motor. Also, the value is maintained so that the output voltage does not rise due to causing regenerative power from the inverter side to flow to the input power source when the inverter unit applies a brake to the motor. Control of these operations of the converter unit is normally implemented by a control unit, or the like, thereof reading a voltage value called a “direct current intermediate voltage”, or the like, using a voltage detector.
The “direct current intermediate voltage” means the direct current voltage between the inverter unit and converter unit (the voltage applied to a smoothing capacitor, or the like, provided between the inverter unit and converter unit). It may be supposed that the “direct current intermediate voltage” corresponds to the output voltage of the converter unit.
Also, there is heretofore known technology disclosed in, for example, Japanese Patent Application Publication No. JP-A-2010-8227 (also referred to herein as “PTL 1”).
The invention of PTL 1 is an invention such that the voltage of a battery unit is detected without increasing power consumption due to leakage current, and with a reduction in part cost. A voltage detector circuit that detects the voltage of a battery unit configuring a high voltage battery includes a resistance divider circuit, switching elements, an A/D converter that converts voltage divided by the resistance divider circuit, or the like, into a digital signal, an operation circuit, and the like. Further, for example, by each switching element being switched to on or off, or the like, the voltage of each connection point in the battery unit is caused to be input into the A/D converter in temporal sequence.
Herein, the power conversion system converter unit compatible with the regenerative operation also includes, for example, switching elements such as IGBTs, and also includes a control unit, or the like, that controls the switching on and off (PWM control) of the switching elements. In particular, in the case of this kind of power conversion system having IGBTs or the like, the following problem occurs.
That is, when a failure occurs in the voltage detector that detects the “direct current intermediate voltage” (output voltage), particularly when a detected value lower than the actual voltage value is output, the converter unit attempts to maintain the output voltage at the target value, because of which an output voltage that is actually higher than the target value is generated. For example, when the value detected by the voltage detector (in which a failure is occurring) is 70V, despite the actual value being 100V, with a setting that maintains the output voltage at 100V, the converter unit may generate the actual output voltage value in the region of, for example, 130V.
When the value of the converter unit output voltage exceeds the breakdown voltage of “the IGBTs that are the switching elements configuring the converter unit and inverter unit” due to this kind of voltage detector failure, the elements are destroyed, causing serious damage to the power conversion system.
The invention of PTL 1 is such that no failure in the voltage detector circuit itself is envisaged, and of course, absolutely no consideration is given to detecting a failure in the voltage detector circuit itself.